When the heart is stopped during cardiovascular surgery, it is necessary to provide for the function of the heart and/or the lungs artificially. The patient's blood is conducted out of the body from the venous system for oxygenation and filtration and is then pumped back into the body and the arterial system. Such extracorporeal arrangements typically include a reservoir, typically called a venous reservoir, to store a certain volume of blood. Often, the reservoir receives blood from the main attachment to the venous circulation, and "cardiotomy" blood collected by suction from the surgical site. The venous reservoir provides a volume buffer for the extracorporeal system, and also a measure of air bubble removal.
It is known to provide venous reservoirs with rigid walls, and also to provide venous reservoirs which have flexible walls. Flexible venous reservoirs, constructed in the form of a bag or pouch of flexible, polymeric material have the advantage of providing a smooth, even flow of blood from an inlet to an outlet. This is useful since blood is a fragile substance, and likely to be adversely affected if allowed to lie stagnant in any portion of the extracorporeal circuit. Flexible venous reservoirs typically have one or more vents at the top to allow the venting off of gas bubbles which have entered the blood upstream of the reservoir (e.g., in the cardiotomy blood).
It is also known that it can be advantageous to support a flexible venous reservoir in an assembly which physically constrains the flexible walls of the reservoir so as to limit the maximum blood volume which may be contained in the reservoir. One such arrangement is disclosed in U.S. Pat. Nos. 5,352,218; 5,693,039 and 5,720,741, where a flexible venous reservoir is constrained between a bracket frame and a front plate. However, in the disclosed arrangement, the front plate covers substantially the entire front and back surface of the flexible reservoir, leaving no access to the reservoir for manipulation to expedite air bubble removal without releasing the entire reservoir from restraint.
U.S. Pat. No. 5,573,526 discloses another flexible reservoir and a volume restricting holder assembly comprising a rigid base plate and a volume restriction plate, which define a V-shaped gap of variable size for receiving the flexible reservoir.